Constitutive Modeling of the Tensile Behavior of Al-TWIP Steel
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SEVERAL types of advanced high-strength steels exhibiting high strength and superior formability are being developed for automotive applications to achieve both an improved passenger safety and a reduced weight of the body-in-white. High Mn austenitic Twinninginduced plasticity (TWIP) steel is one of the most promising newly developed automotive steels as a result of its superior combination of strength and ductility.[1–3] In low stacking fault energy (SFE) austenitic steels, it is generally accepted that deformation twinning results in an increased strain-hardening rate by the creation of twin boundaries that act as effective obstacles to dislocation glide by a dynamic Hall–Petch effect.[3] As the SFE decreases, the stacking faults get wider and cross slip becomes increasingly more difficult. In these conditions, mechanical twinning becomes a more favored deformation mode. In the low SFE range, both dislocation slip and twinning contribute to plastic strain. The excellent strain-hardening properties of TWIP steels containing appreciable amounts of solute C, typically more than 0.5 mass pct, can, in certain cases, JINKYUNG KIM, Graduate Student, and BRUNO C. DE COOMAN, Professor, are with the Materials Design Laboratory, Graduate Institute of Ferrous Technology, Pohang University of Science and Technology, Pohang 790-784, South Korea. Contact e-mail: [email protected] YURI ESTRIN, Professor and Director, is with the Center for Advanced Hybrid Materials, Department of Materials Engineering, Monash University, Clayton, VIC 3800, Australia, and is also with the CSIRO Division of Process Science and Engineering, Clayton, VIC, Australia. HOSSEIN BELADI and ILANA TIMOKHINA, Senior Research Academics, are with the Center for Material and Fibre Innovation, Deakin University, Geelong, VIC 3216, Australia. KWANG-GEUN CHIN and SUNG-KYU KIM, Researchers, are with the Technical Research Laboratories, POSCO Gwangyang Works, Gwangyang, Jeonnam 545-090, South Korea. Manuscript submitted September 14, 2010. Article published online October 5, 2011 METALLURGICAL AND MATERIALS TRANSACTIONS A
be influenced by dynamic strain aging (DSA). TWIP steels with a considerable amount of interstitial carbon in solid solution exhibit a serrated flow curve. It is likely that solute carbon atoms may cause DSA. Some authors have suggested that DSA resulted in the high strainhardening rates for TWIP steel.[4] Chen et al.[5] reported that DSA caused a pronounced localization of plastic deformation in Fe18Mn0.6C TWIP steel. A previous study by the present authors[6] revealed that DSA also occurred in Fe18Mn1.5Al0.6C TWIP steel even though Al additions lead to a pronounced reduction of the DSA effect by increasing the critical strain for the onset of serrations on the stress–strain curve. Many studies have dealt with modeling the tensile behavior of TWIP steels, especially Fe22Mn0.6C TWIP steel.[3,7–9] In these earlier studies, the contribution of DSA to the flow stress of TWIP steel was disregarded even though the occurrence of DSA was clearly vis
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